1. Field of The Invention
This invention relates to phenolic imides which are useful as antioxidant stabilizers for organic materials, including a large variety of synthetic polymers, typically subject to thermooxidative degradation. The antioxidant effectiveness of the stabilizers of the present invention is enhanced by the deactivating potential of the amido-imide moiety towards metals or metal ions that frequently contaminate polymer compositions and serve to catalyze thermal degradation.
2. Description of Prior Art
Degradation of a polymeric material, such as plastic, generally occurs when the polymeric material is exposed to a high temperature environment either during processing or in final application. This degradation is evidenced by discoloration, cracking and loss of mechanical properties of the polymeric material. To help prevent these degradative effects, a multitude of heat stabilizer additives are commercially available which can be added to the polymeric material. For example, polymeric materials may be protected against thermooxidative degradation by adding an antioxidant stabilizer to the polymeric material to inhibit or terminate free radical induced chain reactions. This type of stabilizer interrupts the propagation step in the oxidative degradation mechanism and thereby reduces the overall oxidation rate. An example of such an antioxidant stabilizer to be added to the polymeric material is a hindered phenol.
Transition metals, such as copper, iron, cobalt and manganese and ions thereof are generally known to accelerate the rate of oxidation by catalyzing the decomposition of hydroperoxides to radical species. See Encyclopedia of Polymer Science and Engineering, John Wiley & Sons, New York, N.Y., 1985, Vol. 2, p. 75. Therefore, a metal deactivator compound may be added to the polymeric material to inhibit thermal degradation. The metal deactivator generally forms complexes with the aforementioned metals or metal ions to block their catalytic activity. Oxamide and hydrazine derivatives are generally the types of compounds used as metal deactivators.
Coupling hindered phenols to metal deactivating moieties is generally an effective method for enhancing the thermooxidative stability of both polymeric and non-polymeric organic materials. This coupling strategy is well known in the art. For example, U.S. Pat. No. 3,706,798 of Dunnenberger and U.S. Pat. No. 3,734,884 of Biland disclose phenolic bisoxalic acid diamides as stabilizers for polypropylene.
U.S. Pat. No. 4,038,247 of Muller et al. discloses that phenolic diacyl dihydrazides are particularly effective for stabilizing polyolefins against metal catalyzed oxidation.
U.S. Pat. No. 4,145,556 of Hirsh et al. teaches the use of N,N'-bis[(alkylhydroxyphenyl)alkanoylhydrocarbyl] oxamides as stabilizers for polyolefins against degradation from thermal and metal catalyzed oxidation. Several commercial antioxidants contain similar chemical structures. For example, N,N'-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamoyl)hydrazine is one such compound and is available from Ciba-Geigy. Another structurally similar compound is 2,2'-oxamidobisethyl(3,5-di-t-butyl-4-hydroxyhydrocinnamate), commercially available from Uniroyal.
Other hydrazine-type linkages that have been shown to be effective metal deactivators are N-(amido)imide linkage, prepared by reacting hydrazides with compounds containing a cyclic anhydride group. Yoshikawa et al. demonstrated the metal deactivating capability of such compounds in U.S. Pat. Nos. 3,933,736 and 3,956,332 by incorporating N-(salicyloylamino)imides into polyolefin compositions.
Hindered phenolic hydrazides have also been reacted with certain types of cyclic anhydrides to form N-(amido)imide antioxidant stabilizers. Hansen has coupled such hindered phenols to halogenated norbornene-2,3-dicarboxylic anhydrides (U.S. Pat. No. 4,514,533) and to halogenated phthalic anhydrides (U.S. Pat. No. 4,520,146) to obtain antioxidant/flame retardant additives.
Helwig et al. (German Offenlegungsschrift 3,500,058) have prepared other N-(amido)phthalimides from hindered phenolic hydrazides and substituted phthalic anhydrides as antioxidants for polypropylene. U.S. Pat. No. 4,874,803 of Baron et al. discloses preparing a series of bis N-(amido)imide antioxidants from bis-anhydride substrates as additives for a variety of polymers.